Method for manufacturing a steel friction lamella for a friction coupling

ABSTRACT

A method for manufacturing a friction lamella by way of the following steps:
         a steel sheet is supplied, which is provided with macrostructuring on at least one face,   a friction lamella blank is separated out from the steel sheet and further processed into an annular lamella body.

The invention relates to a method for manufacturing a steel friction lamella for a friction coupling.

Friction lamellae and friction couplings comprising these friction lamellae are used to establish a frictional or non-positive connection between at least two shafts. Examples are switchable couplings, such as are used for example in a transmission of a motor vehicle, or non-switchable couplings, such as are used for example as a differential lock in a motor vehicle differential transmission.

Conventionally, in a friction system of this type, a steel lamella body is used, which is provided with a sintered coating or a molybdenum coating on the primary faces thereof (in other words the front and rear faces). These are generally manufactured in a multi-layer construction. Overall, this leads to a complex manufacturing process and increased manufacturing costs.

The object of the invention is to provide a friction lamella which is distinguished by a good price/performance ratio.

To achieve this object, the invention proposes a method for manufacturing a friction lamella in which a steel plate is supplied which is provided with macrostructuring on at least one side. A friction lamella blank is separated out from the steel sheet, and is further processed into an annular lamella body.

A friction coupling containing at least one friction lamella manufactured by the method according to the invention uses a pure steel/steel friction pair. According to the invention, it has been found that the coatings which were previously always considered necessary can be dispensed with. The method according to the invention is particularly advantageous in relation to the manufacturing costs, since the starting material for the friction lamellae can be provided in the form of a sheet steel coil, which is already provided with the desired macrostructuring. It is therefore not necessary to process each friction lamella individually so as to provide macrostructuring.

The term “macrostructuring” refers herein to structuring of which the dimensions (in other words the depth or width of the structures) are much greater than the dimensions of microscopic structurings (for example the surface configuration due to some unavoidable surface roughness). Macrostructuring is distinguished in particular in that it is visible to the naked eye. The advantage of macrostructuring is that it improves the lubrication of the friction areas.

A preferred embodiment provides that the friction lamella blank is annealed. This increases the service life.

It is preferably provided that the macrostructuring is rolled onto both sides of the steel sheet. This makes it possible only to use the macrostructuring for every second lamella of the friction coupling, whilst the lamellae positioned in between can be configured with a smooth surface. This reduces the manufacturing costs overall.

A preferred embodiment provides that the macrostructuring on one side is rolled on offset from the macrostructuring on the other side. This prevents the friction lamella from being weakened by the resulting low wall thickness at the points where depressions of the macrostructuring “overlap one another”.

The offset in the macrostructurings may for example be achieved in that different divisions are used on one face and on the other. It is also possible to arrange the rollers used for rolling on the macrostructuring mutually offset in the circumferential direction, in such a way that the rolled-on patterns are mutually offset.

A honeycomb pattern has been found to be a particularly suitable pattern for the macrostructuring, since it can be rolled on in a simple manner and the orientation of the macrostructuring does not need to be taken into account when the lamella body is separated out from the steel sheet. Moreover, a lubricant can be held in the pockets formed at regular intervals.

A preferred embodiment of the invention provides that the friction areas are the outer face of the lamella body. In other words, the lamella body is not produced with steel friction elements, and instead is produced to the thickness which the friction lamellae are subsequently to have.

The macrostructuring may have a structure depth in the range of 0.05 to 0.9 mm, in particular in the range of 0.2 to 0.4 mm. These values have been found to be a good compromise.

The width of a structural element may be in the range of 0.1 to 4 mm. These values are also advantageous.

Preferably, at least one clearance in the lamella body is provided, in other words an opening extending continuously from one friction area to the other. A clearance of this type improves the provision of the friction areas with a lubricant.

Depending on the conditions of use, it may be sufficient to use a single clearance. A comparatively large number of clearances may also be used, for example 40. For the majority of applications, the number of clearances is in the range of 3 to 11.

The clearance may be configured as a slit. This makes it possible to provide a comparatively large region of the friction area with lubricant without sacrificing much of the friction area for this purpose. A further advantage of slits is that they prevent friction lamellae from deforming as a result of thermal stresses and/or thermal expansions.

Depending on the use condition, the slit may be arranged completely inside a friction lamella, in other words start and end at a distance from a circumferential edge of the friction lamella, or extend into the friction area from a circumferential edge and end at a distance from a circumferential edge, or else extend completely through a friction area, in other words from one circumferential edge to the other.

Preferably, the slit has a width in the range of 0.1 to 5 mm, in particular in the range of 1.3 to 3 mm. These values represent a good compromise between supplying the friction areas with lubricant and a minimum loss of friction area.

One embodiment of the invention provides that the slit is at an angle of 0° to 70° to a radius of the friction lamella. In this orientation, centrifugal effects can be used to distribute lubricant well between the friction lamellae.

In principle, it may be provided that slit extends straight, curved or in a wave.

It is preferably provided that the clearance is located at least in part in a region of the lamella body at a distance from a circumferential edge corresponding to more than 10% of the width of the lamella body. This ensures that the lubricant is also distributed in the centre of the friction area and not only at the circumferential edge of the friction lamellae.

Preferably, the lamella body forms a flat, planar disc. In alternative embodiments, it is also possible for the friction lamellae to have a slightly frustum-like shape.

One embodiment provides that the lamella body is composed of a plurality of segments. These may be welded, glued or merely positively engaged together.

The friction lamella blank may be separated off from the steel sheet as a single-piece blank, for example by laser cutting, waterjet cutting, fine blanking or punching.

To reduce the wear on the friction areas of the friction lamellae and also to prevent local wear, it is preferably provided that the friction lamella blank is annealed. This may in particular take place by nitriding or nitrocarburisation. It is also possible to provide the friction lamella blank with the desired hardness by plasma nitriding, salt bath annealing or other suitable methods.

One embodiment of the invention provides that microstructuring is superposed on the macrostructuring. As a result, the frictional properties can be improved in the desired manner.

The microstructuring may be introduced by a grinding process, for example using a belt sander. This method is distinguished by a low complexity and low costs.

In the following, the invention is disclosed by way of various embodiments, which are shown in the appended drawings, in which:

FIG. 1 is a schematic sectional view of a friction coupling comprising friction lamellae manufactured by the method according to the invention;

FIG. 2 shows a friction lamella according to a first embodiment in a front view, a rear view, a side view and an enlarged detail;

FIG. 3 shows a friction lamella according to a second embodiment in views corresponding to those of FIG. 2;

FIG. 4 shows a friction lamella according to a third embodiment in views corresponding to those of FIG. 2;

FIG. 5 shows a friction lamella according to a third embodiment in views corresponding to those of FIG. 2;

FIG. 6 schematically shows the steps of the method according to the invention.

FIG. 1 schematically shows a friction coupling 2 which serves to couple a first shaft 3 to a second shaft 4 in a frictional fit.

The shaft 3 is provided on the external circumference thereof with an entraining geometry which comprises a plurality of grooves 5. The shaft 4 is provided with a cage-like or cup-like recess 6, which is likewise provided on the inner face thereof with an entraining geometry which comprises a plurality of grooves 7. Between the portions of the shaft 3 and shaft 4 provided with the grooves 5, 7, there is a friction lamella packet 8 consisting of a plurality of lamellae of a first and a second type.

The entraining geometries of the shafts 3, 4 may be toothings.

Each lamella has the underlying form of a circular ring. The lamellae of the first type are coupled to the shaft 3 so as to be rotationally engaged but axially displaceable, and thus have an entraining geometry on the inner circumferential edge thereof, and the friction lamellae of the second type are coupled to the shaft 4 so as to be rotationally engaged but axially displaceable, and thus have an entraining geometry on the outer circumferential edge.

The friction lamella packet 8 is compressed in the axial direction, in such a way that the friction lamellae are positioned biased against one another. This bias may be produced in various ways. By way of example, a spring 9 is shown in this case.

FIG. 2 shows a friction lamella 10 according to a first embodiment. This is a lamella of the second type of the friction lamella packet 8 of FIG. 1, since the friction lamella 10 is provided with an entraining geometry 12 on the outer circumference thereof. In this case, the entraining geometry 12 is formed by a plurality of radially projecting teeth (and clearances located between the teeth). The teeth of the entraining geometry 12 engage in the grooves 7 of the clearance 6.

The friction lamella 10 comprises a lamella body 14 consisting of steel.

The lamella body 14 comprises a front face 16 and a rear face 18. These form the friction areas of the friction lamella 10. The lamella body 14 is thus not provided with a coating and also not configured as a composite part made of a plurality of layers.

In the shown embodiment, the front face 16 is configured smooth (apart from the microscopic surface roughness), whilst the rear face 18 is provided with macrostructuring 20.

In this case, the macrostructuring 20 is formed as a honeycomb pattern, which has a depth in the range of 0.05 to 0.9 mm and in particular in the range of 0.2 to 0.4 mm. The width of a structural element (in other words the distance between adjacent projecting regions of the honeycomb pattern or the distance between the centre points of adjacent depressions in the honey comb pattern) is in the range of 0.1 to 4 mm.

As can be seen in particular in FIG. 2b , the macrostructuring extends over the entire friction area on the rear face 18 of the friction lamella, in other words into the region of the entraining geometry 12.

The friction lamella 10 is provided with a plurality of clearances 30, which in this case are each in the form of a slit. Each slit 30 extends in a straight line and from the inner circumferential edge of the lamella body 14. The width b of each slit 30 is in the range of 0.1 to 5 mm and preferably in the range of 1.3 to 3 mm. Each slit 30 extends obliquely with respect to a radius r of the lamella body, the angle being approximately 30° in the embodiment shown.

In this case, each slit 30 extends from the inner circumferential edge to the outer circumferential edge, and ends at a distance from the outer circumferential edge, the distance being approximately 25% of the width of the lamella body.

The radially outer end of each slit 30 is configured rounded in a semicircle shape.

It has been found that the combination of the slit with the macrostructuring has an advantageous effect on the vibration properties of the friction lamellae.

FIG. 3 shows a second embodiment of the friction lamella. For the features known from the first embodiment, the same reference numerals are used, and in this regard reference is made to the above explanations.

The difference between the first and the second embodiment is that in the second embodiment the front face 16 of the friction lamella is also provided with the macrostructuring 20.

In the embodiment shown, the same macrostructuring is used on the front face 16 and the rear face 18.

In this case too, a positive effect of the slits on the vibration properties of the friction lamellae was observed.

FIG. 4 shows a third embodiment of the friction lamella 10. For the features known from the previous embodiments, the same reference numerals are used, and in this regard reference is made to the above explanations.

The difference between the first and the third embodiment is that in the third embodiment a single clearance 30 is used, which in this case extends as a continuous slit from the inner circumferential edge to the outer circumferential edge of the lamella body 14. The orientation relative to a radius corresponds to the orientation of the slit 30 in the first embodiment.

The slit 30 is not disadvantageous for the strength of the friction lamella 10, since the lamella can be braced in the recess 6 thereof.

FIG. 5 shows a fourth embodiment. For the features known from the previous embodiments, the same reference numerals are used, and in this regard reference is made to the above explanations.

The difference between the first and the third embodiment is that in the third embodiment clearances 30 are used which start and end within the lamella body 14, in other words do not form an interruption to the inner or outer circumferential edge. By way of example, the following are shown as clearances in this case: a straight slit orientated at an angle of 30° to a radius of the friction lamella, two circular openings, and a wave-shaped slit which extends over a circumferential range of somewhat less than 90°.

The various features of the embodiments shown in FIGS. 2 to 5 may be combined with one another in a manner dependent on the application. For example, the macrostructuring which is merely provided on one face of the friction lamella in the first, third and fourth embodiments may also be used on the other face.

All of the features of the friction lamellae shown in FIGS. 2 to 5 may of course also be used in friction lamellae of a first type, in other words in friction lamellae which have the entraining geometry 12 thereof on the inner circumferential edge thereof.

In the following, the method for manufacturing the friction lamella is disclosed by way of FIG. 6.

A steel sheet 1, is used as the starting material, and the desired macrostructuring is rolled onto it. For this purpose, two schematically indicated rollers 2 are provided, on the surface of which a plurality of structural elements 3 are arranged.

When the macrostructuring is rolled on, care is taken that the macrostructuring on the upper face of the steel sheet is offset from the macrostructuring on the lower face. In the example of a honeycomb pattern, care is thus taken that the pockets on the upper face and the lower face are not positioned coincidently opposite one another, since this would lead to undesired weakening of the lamella blank and also of the subsequent friction lamella.

The desired offset in the two macrostructurings can be achieved in that different step sizes, in other words different distances from pocket to pocket, are used on the upper face and the lower face, or in that the structural elements 3 on the rollers 2 are orientated mutually offset and this offset is maintained during rolling.

The steel sheet provided with the macrostructuring can subsequently be wound up, in such a way that it is supplied as a coil for the subsequent processing steps.

Subsequently, the lamella blanks 4 are separated out from the steel sheet 1. In FIG. 6, this is indicated by two punching tools 5. However, the lamella blanks may also be separated out from the steel sheet by laser cutting, waterjet cutting, fine blanking or other suitable methods.

Microstructuring is superposed on the macrostructuring provided in the lamella blanks 4. It may in particular be introduced by grinding, for example using a belt sander. This is indicated by belt sanders 6 which grind the surface of the lamella blank 4 being conveyed onwards on a conveyer belt 7. In this case, the lamella blank is rotated between the first and the second grinding process; this is indicated as method step 8.

After the microstructuring is introduced, the lamella blanks 4 may additionally be annealed or further processed in some other manner. These further processing steps are indicated by reference numeral 9.

The particular advantage of this method is that no coating or cover has to be applied to the lamella blank, resulting in very low manufacturing costs overall. 

1. A method for manufacturing a friction lamella comprising the following steps: a steel sheet is supplied, which is provided with macrostructuring on at least one face, a friction lamella blank is separated out from the steel sheet and further processed into an annular lamella body.
 2. The method according to claim 1, characterized in that the friction lamella blank is annealed.
 3. The method according to claim 1, characterized in that the macrostructuring is rolled onto both faces of the steel sheet.
 4. The method according to claim 3, characterized in that the macrostructuring rolled onto one face is offset from the macrostructuring on the other face.
 5. The method according to claim 1, characterized in that the macrostructuring is a honeycomb pattern.
 6. The method according to claim 1, characterized in that the macrostructuring has a structure depth in the range of 0.05 to 0.9 mm.
 7. The method according to claim 1, characterized in that a structural element has a width in the range of 0.1 to 4 mm.
 8. The method according to claim 1, in that the lamella body is provided with at least one clearance.
 9. The method according to claim 8, characterized in that that the lamella body is provided with from 1 to 40 clearances.
 10. The method according to claim 8, characterized in that the clearance is a slit.
 11. The method according to claim 10, characterized in that the slit starts and ends at a distance from a circumferential edge of the friction lamella.
 12. The method according to claim 10, characterized in that the slit starts at a circumferential edge of the friction lamella and ends at a distance from a circumferential edge of the friction lamella.
 13. The method according to claim 10, characterized in that the slit extends from one circumferential edge of the friction lamella to the other circumferential edge of the friction lamella.
 14. The method according to claim 10, characterized in that the slit has a width in the range of 0.1 to 5 mm.
 15. The method according to claim 10, characterized in that the slit is at an angle of 0 to 70° to a radius of the friction lamella.
 16. The method according to claim 10, characterized in that the slit extends straight, curved or in a wave.
 17. The method according to claim 8, characterized in that the clearance is located at least in part in a region of the lamella body at a distance from a circumferential edge corresponding to more than 10% of the width of the lamella body.
 18. The method according to claim 1, characterized in that the lamella body forms a flat, planar disc.
 19. The method according to claim 1, characterized in that the lamella body is composed of a plurality of segments.
 20. The method according to claim 1, characterized in that microstructuring is superposed on the macrostructuring.
 21. The method according to claim 20, characterized in that the microstructuring is introduced by a grinding process. 